Bentho‐Pelagic Decoupling: The Marine Biological Carbon Pump During Eocene Hyperthermals. Issue 3 (25th March 2021)

• Record Type: Journal Article
• Authors: Griffith, Elizabeth M.; Thomas, Ellen; Lewis, Angela R.; Penman, Donald E.; Westerhold, Thomas; Winguth, Arne M. E.
• Is Part Of: Paleoceanography and paleoclimatology. Volume 36:Issue 3(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-03-25
• Subjects: barium -- benthic foraminifer -- Eocene -- export production -- hyperthermal -- remineralization; Paleoceanography -- Periodicals; Paleoclimatology -- Periodicals; 551.46
• DOI: 10.1029/2020PA004053
• Languages: English
• ISSNs: 2572-4517

Abstract

Abstract: Future environmental change may profoundly affect oceanic ecosystems in a complex way, due to the synergy between rising temperatures, reduction in mixing and upwelling due to enhanced stratification, ocean acidification, and associated biogeochemical dynamics. Changes in primary productivity, in export of organic carbon from the surface ocean, and in remineralization deeper in the water column in the so‐called "twilight zone" may substantially alter the marine biological carbon pump, thus carbon storage in the oceans. We present different proxy records commonly used for reconstructing paleoproductivity, and re‐evaluate their use for understanding dynamic change within and between different constituents of the marine biological pump during transient global warming episodes in the past. Marine pelagic barite records are a proxy for carbon export from the photic and/or mesopelagic zone, and are not positively correlated with benthic foraminiferal proxies for arrival of organic matter to the seafloor over three early Eocene periods of global warming (Ocean Drilling Program Site 1263, SE Atlantic). These two proxies reflect processes in different parts of the water column, thus different components of the biological pump. An increase in temperature‐dependent organic carbon remineralization in the water column would have caused decreased arrival of food at the seafloor, starving the benthic biota and explaining the differences between the proxies, and may have led to ocean deoxygenation. Carbon cycle modeling demonstrates the feasibility of enhanced water‐column remineralization to explain both Site 1263 records, suggesting that this mechanism amplifies p CO2 increase, representing a positive feedback during hyperthermal warming. Plain Language Summary: A major challenge in understanding the response of the oceanic carbon cycle to ongoing global warming is predicting how much organic carbon is sequestered in the deep ocean waters, where it may remain for centuries, and in sediments, where it may be stored for millions of years. We present evidence from the deep‐sea sedimentary record of barite and benthic foraminifera over three transient Eocene extreme warm periods to show that more organic matter was remineralized within the water column during global warming (relative to background levels), thereby increasing the total oceanic reservoir of dissolved inorganic carbon, while decreasing carbon sequestration in sediments. Key Points: Remineralization is enhanced in twilight zone and organic matter arrival at seafloor reduced during Eocene warm periods in SE Atlantic Increase in temperature‐dependent remineralization can explain lack of correlation between barite and benthic foraminiferal records Carbon cycle modeling confirms enhanced water‐column remineralization as a positive feedback to hyperthermal warming